Process for chemical reactions involving cyanohydrins

ABSTRACT

The present invention provides a method for minimizing the decomposition of cyanohydrins in exothermic chemical reactions involving cyanohydrins. The method comprises providing a reaction medium and reactants to a tubular reactor having internal mixing means, mixing the reaction medium and reactants to form a homogenous reaction mixture, removing heat from the reaction process and reacting the reactants to produce a mixed product having a bulk temperature. The method may further comprise cooling the reaction medium to a temperature from 1-10° C. cooler than the bulk temperature of the mixed product prior to providing the reaction medium to the tubular reactor.

This non-provisional application is a divisional of non-provisional U.S.patent application Ser. No. 11/268,372, filed Nov. 7, 2005, now allowed,benefit of which is claimed under 35 U.S.C. §120 and which in turnclaims benefit under 35 U.S.C. §119(e) of U.S. provisional ApplicationNo. 60/630,872, filed Nov. 24, 2004, priority benefit of which is alsoclaimed for the present application.

The present invention relates to minimizing the thermal decomposition ofcyanohydrins in chemical reactions involving cyanohydrins, such ashydrolysis reactions of acetone cyanohydrin, whereby overall productyields are increased.

There are many chemical processes which involve cyanohydrins, either asreactants or products. For example, well-known commercial processes forthe production of methacrylic acid (“MAA”) and esters thereof, such asmethyl methacrylate (“MMA”) and butyl methacrylate (“BMA”), from acetonecyanohydrin typically involve a series of reactions, including theinitial hydrolysis reaction of acetone cyanohydrin with sulfuric acid.The process for production of MAA and esters of MAA also includescracking of the hydrolysis products and further reaction, such as anacidification reaction to form MAA, or an esterification reaction toform esters of MAA. In addition, acetone cyanohydrin itself is theproduct of the reaction of acetone with hydrogen cyanide. The commercialmarket for MAA and esters thereof is extremely cost-sensitive and,therefore, any improvement in product yield, however slight, can resultin significant cost-savings.

It is known that cyanohydrins are susceptible to decomposition in thepresence of strong acids (e.g., sulfuric or phosphoric acid) or strongbases (e.g., caustic or diethylamine) to form hydrogen cyanide and otherdecomposition products (depending upon the nature of the cyanohydrin) atelevated temperatures, such as, for example, greater than about 70° C.Decomposition of cyanohydrin in reactions where the cyanohydrins arethemselves the desired products results directly in decreased productyields. Decomposition of cyanohydrin in reactions where the cyanohydrinsare intermediates or reactants in further reactions, such as in theproduction of MAA and its esters, indirectly results in decreasedproduct yields, since a portion of the cyanohydrin is destroyed ratherthan being consumed by further reactions to produce the intended,desired reaction products. Thus, minimization of decomposition ofcyanohydrin is an ongoing goal of chemical manufacturers whose reactionsinvolve cyanohydrins.

It is also known that while higher temperatures generally increase thereaction rate of chemical reactions involving cyanohydrins, suchreactions are also typically exothermic. Thus, in view of the potentialfor decomposition of cyanohydrins at high temperatures, strict controlof the reaction temperature in processes involving cyanohydrins isimportant to maintain reaction rates while minimizing decomposition ofthe cyanohydrins.

One method known in the art for strictly controlling the reactiontemperature of reactions involving cyanohydrins, including thehydrolysis reaction of acetone cyanohydrin with sulfuric acid, is tocontain the reaction zone (where the reaction occurs) in one or morecontinuous stirred tank reactor (“CSTR”). CSTRs are typicallywell-agitated kettles or tanks and, for various reasons, a reactionprocess may include two or more CSTRs connected in series. CSTRs areoften selected to contain reaction zones of particular chemicalreactions requiring homogeneity because they are well-known andunderstood in the art to provide a homogenous reaction environment,i.e., where the reaction mixture composition and the reactiontemperature are homogenous throughout the reaction zone. This means thatthe composition and temperature at which the reaction takes place withina CSTR is understood and assumed in the art to be the same as thecomposition and temperature at all locations within the CSTR, as well asthe CSTR exit stream. Such uniformity of temperature and composition ishelpful for optimizing the yield of chemical reactions, including thoseinvolving cyanohydrins, such as hydrolysis reactions of acetonecyanohydrin, in accordance with prior art methods.

For example, the Encyclopedia of Chemical Technology, by Kirk-Othmer,4^(th) Edition, Vol. 16, John Wiley & Sons, 1995, pp. 16-18 and FIG. 4,teaches the preparation of MAA and its esters using the well-knownprocess which begins with hydrolyzing acetone cyanohydrin with sulfuricacid in a CSTR. Similarly, U.S. Patent Publication No. 2003/0208093 (US'093) teaches a process for production of MAA and its esters wherein aseries of two to three CSTR's are used for the hydrolysis reaction ofacetone cyanohydrin with sulfuric acid. US '093 teaches that thehydrolysis reaction temperature is typically 70° C. to 135° C. (whichmeans that the temperature of the bulk reaction mixture in the CSTR is70° C. to 135° C.). According to the teachings of both documents, thehydrolysis reaction produces a hydrolysis mixture comprisingα-sulfatoisobutyramide (“SIBAM”), α-hydroxyisobutyramide (“HIBAM”), anda lesser amount of methacrylamide (“MAM”). The hydrolysis mixture issubjected to a cracking reaction in which the SIBAM and HIBAM areconverted to more MAM. The resulting MAM product may then be furtherreacted with water to produce MAA and with alkanols (e.g., methanol,butanol) to produce esters of MAA (e.g., MMA, BMA).

However, surprisingly and contrary to the general knowledge in the art,it has been discovered that where CSTRs are used in reactions involvingcyanohydrins, such as the hydrolysis reaction of acetone cyanohydrinwith sulfuric acid, persistent regions of high temperature occur in andaround the location where the reactant feed is introduced into the CSTR(hereinafter, referred to as the “point of addition”). These localizedregions of high temperature (herein referred to as “hot spots”) may beup to 10° C., or even up to 20° C., higher than the otherwise uniformtemperature of the bulk reaction mixture within the CSTR. These hotspots promote thermal decomposition of the cyanohydrin, thereby leadingto a significant source of decreased product yields.

Thus, for example, in a process for the production of MAA and itsesters, which involves the hydrolysis reaction of acetone cyanohydrinwith sulfuric acid in a CSTR, where the reaction temperature ismaintained within the presumably safe range of 80° C. to 90° C., the hotspot at the point of addition of the acetone cyanohydrin is greater than90° C., which promotes the decomposition of the acetone cyanohydrin overthe production of the preferred hydrolysis products (i.e., SIBAM, HIBAMand MAM) that are required for the further downstream reactions andultimate production of MAA and its esters. Such irrecoverable yieldlosses can be as high as 3% and are, therefore, quite significant to theoverall MAA and MAA ester production processes.

Out of all of the process variables in the hydrolysis reaction discussedabove, studies have revealed that reaction temperature is the mostsignificant with respect to acetone cyanohydrin decomposition. Onaverage, laboratory experimentation by the applicants has revealed thatacetone cyanohydrin decomposition decreases hydrolysis yield by about 1%for each 10° C. increase in hydrolysis reaction temperature. Forexample, in hydrolysis reactions of acetone cyanohydrin with sulfuricacid, conducted in a laboratory-scale CSTR, it was determined that anincrease in the hydrolysis temperature of 10° C., from 85° C. to 95° C.,resulted in an incremental 1% product yield loss.

Additionally, rapid and thorough mixing of the reactants with thereaction medium in the reaction zone is important for various reasons,including facilitating temperature control in reactions involvingcyanohydrins. U.S. Pat. No. 5,763,687 discloses that thorough mixing ina chemical reaction for producing aromatic mononitro compounds can beachieved by the use of a tubular reactor having a particular internalconfiguration. More particularly, a plurality of twisted tabular membersare arranged and positioned within the tubular reactor such that whenreactants are fed to the reactor they are efficiently mixed as they passthrough the reactor.

In view of the foregoing difficulties and shortcomings of conductingreactions involving cyanohydrins using CSTRs, which results in the newlydiscovered formation of a detrimental hot spot at the point of additionto the CSTR, there is a need for a method of conducting such reactionswhich minimizes the potential for decomposition of the cyanohydrins. Themethod of the present invention achieves this goal by using a reactorapparatus that ensures rapid and thorough mixing of the reactants withthe reaction medium in the reaction zone and by manipulating thereaction temperature.

In a general embodiment of the present invention, a method forminimizing decomposition of cyanohydrins in an exothermic reactionprocess involving cyanohydrins is provided. The method comprises thesteps of: (a) providing a reaction medium to a tubular reactorcontaining at least one reaction zone therein and having internal mixingmeans positioned in the at least one reaction zone; (b) providing one ormore reactants to the tubular reactor; and (c) mixing the reactionmedium with the one or more reactants in the at least one reaction zone,thereby forming a bulk reaction mixture having a substantiallyhomogenous composition and a substantially homogenous reactiontemperature. The exothermic reaction produces a quantity of heat and,therefore, the method of the present invention further comprises (d)removing a quantity of heat from the exothermic reaction process, thequantity of heat being equivalent to the quantity of heat produced bythe exothermic reaction process; and (e) reacting the one or morereactants in the at least one reaction zone to produce a mixed producthaving a bulk temperature.

The tubular reactor may, in fact comprise two or more tubular reactorsarranged in parallel or in series with one another. The internal mixingmeans of the tubular reactor may be at least one device selected fromthe group consisting of: static mixers, orifice plates, venturis, jetmixers, eductors, perforated plates, spargers, agitators, rotary mixers,high-velocity circulation loops, and spray nozzles. Furthermore, thereaction medium and the one or more reactants may be provided to thetubular reactor at a ratio of reaction medium:reactants of between 2:1and 200:1.

In a particular embodiment of the present invention, the step ofremoving a quantity of heat may be performed by cooling the reactionmedium to a temperature between 1° C. and 10° C. less than the bulktemperature prior to providing the reaction medium to the tubularreactor.

In another particular embodiment of the present invention, a first oneof the one or more reactants may be provided to the tubular reactor inat least one of a plurality of points of addition by a plurality ofinjector devices positioned circumferentially about the tubular reactorapparatus. The step of mixing the reaction medium with the one or morereactants to form a homogenous bulk reaction mixture may beaccomplished, at least in part, by selecting and using one or more ofthe plurality of injector devices to provide the at least a first one ofthe one or more reactants to the tubular reactor.

In still another embodiment of the present invention, the exothermicreaction process involving cyanohydrins is a hydrolysis reaction,wherein a first reactant comprises acetone cyanohydrin, and a secondreactant comprises an acid selected from the group consisting of:sulfuric acid, oluem and mixtures thereof. In this embodiment, the molarratio of acid:acetone cyanohydrin present in the bulk reaction mixturemay be in the range of from 1.3:1 to 1.9:1. Additionally, in thisembodiment, the mixed product of the hydrolysis reaction may compriseone or more products selected from the group consisting of:α-sulfatoisobutyramide, α-hydroxyisobutyramide, and methacrylamide; andthe method may further comprise: (f) thermally converting the mixedproduct from the hydrolysis reaction in a cracker reactor to produce acracker reactor mixture comprising methacrylamide and methacrylic acid;and (g) reacting the cracker reactor mixture in at least one reactorwith a material selected from alkanol and water to produce a monomerselected from methacrylic acid and esters thereof.

Additional features and advantages will become apparent from thefollowing detailed description of various embodiments of the presentinvention, considered in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features, and wherein:

FIG. 1 is a schematic representation of an embodiment of the presentinvention wherein the reaction process is a hydrolysis reaction ofacetone cyanohydrin with acid; and

FIG. 2 is a schematic representation of a known prior art process forhydrolysis of acetone cyanohydrin with acid, provided for comparison.

As discussed hereinabove, cyanohydrins are subject to decomposition whenin the presence of strong acids at elevated temperatures, for example attemperatures greater than about 70° C., thereby resulting in reducedprocess yields. Furthermore, in the context of a hydrolysis reaction ofacetone cyanohydrin (“ACH”) with sulfuric acid, the decomposition ofacetone cyanohydrin to acetone and hydrogen cyanide not only results inreducing the yield of hydrolysis products and, in turn, of thedownstream MAA and MAA ester products, but it can also lead toadditional complications in the hydrolysis system.

For example, the hydrogen cyanide formed by decomposition of acetonecyanohydrin is rapidly hydrolyzed and converted to formamide in thehydrolysis reaction. Subsequently and at a slower rate, the formamidethermally cracks to form carbon monoxide (CO) gas and ammonium sulfatesalt. Unless the product mixture is adequately degassed, the presence ofCO may manifest itself as pump cavitation and may contribute to overallprocess and unit inoperability. Increases in the overall temperature ofthe process can aid in the degassing process, however, increasedhydrolysis reaction temperature leads to increased the levels ofdecomposition of acetone cyanohydrin.

Additionally, under the typical operating conditions described inKirk-Othmer, Encyclopedia of Chemical Technology, acetone is sulfonatedby sulfuric acid to a mixture of mono- and di-sulfonic acids. In thehydrolysis section, acetone monosulfonic acid (“AMSA”) predominates andas the reaction progresses further, acetone disulfonic acid (“ADSA”)increases and becomes predominant. This series of reactions is importantbecause each sulfonation of acetone reaction is accompanied by thestoichiometric generation of water. As is well-known in the art andpointed out in US '093, where water is present in the hydrolysisreaction mixture it will react to convert SIBAM to HIBAM, which is moredifficult and requires higher temperatures to convert to MAM in thesubsequent cracking reaction.

In a general embodiment, the method of the present invention forminimizing decomposition of cyanohydrins in an exothermic reactionprocess involving cyanohydrins, comprises the steps of providing areaction medium to a tubular reactor and providing one or more reactantsto the tubular reactor. The tubular reactor contains at least onereaction zone therein and has internal mixing means positioned in the atleast one reaction zone. The method of the present invention furthercomprises mixing the reaction medium with the one or more reactants inthe at least one reaction zone. This mixing forms a bulk reactionmixture having a substantially homogenous composition and asubstantially homogenous reaction temperature. The method also comprisesremoving a quantity of heat from the exothermic reaction process, wherethe quantity of heat removed is equivalent to the quantity of heatproduced by the exothermic reaction process. The quantities of heatremoved and produced are equivalent, for purposes of the presentinvention, where the quantities are about equal to one another, within +or −10%, or even for example, 1%. Lastly, the method of the presentinvention comprises the step of reacting the one or more reactants inthe at least one reaction zone to produce a mixed product having a bulktemperature. The bulk temperature of the mixed product is optimallymeasured after the reaction has ceased (such as, for example, whensubstantially all of at least one of the one or more reactants has beenreacted) and the mixed product has exited the tubular reactor.

By an exothermic reaction process “involving cyanohydrins” it is meantthat one or more of the reactants and products of the reaction processescomprise one or more cyanohydrins. Moreover, as will be recognized bypersons of ordinary skill, an exothermic reaction is a reaction whichproduces a quantity of heat, where the quantity depends upon a number offactors, including but not limited to, the types and amounts ofreactants and the temperature and duration of the reaction.

The term “cyanohydrins” as used herein means compounds having thegeneral formula:

wherein R and R′ may be the same or different and are selected from thegroup consisting of hydrogen and hydrocarbons. The structure of thehydrocarbons is not particularly limited and may comprise straightchains, branched chains, aromatic rings, etc. and the hydrocarbons maybe saturated, substituted, or unsaturated. In addition, R and R′together may form part of an alicyclic or heterocyclic moiety.

With respect to the tubular reactor, the method of the present inventionincludes embodiments wherein there is more than one tubular reactor, oreven a plurality of tubular reactors (such as, for example, in ashell-and-tube type of reactor apparatus), used to perform theexothermic reaction process involving cyanohydrins. Where more than onetubular reactor is employed, at least one, and preferably all of thetubular reactors contain at least one reaction zone therein and haveinternal mixing means positioned in the at least one reaction zone.

Moreover, the internal mixing means of the tubular reactor is at leastone device selected from the group consisting of: static mixerscomprising static mixing elements, orifice plates, venturis, jet mixers,eductors, perforated plates, spargers, agitators, rotary mixers,high-velocity circulation loops, and spray nozzles. The static mixingelements may be one or more elements selected from the group consistingof blades, pins, baffles, tabular inserts, and other shear-inducingdevices. Such devices and static mixing elements are well known andcommercially available from companies such as Koch-Glitsch, Inc. ofWichita, Kans., Chemineer, Inc. of Dayton, Ohio, and Sulzer ChemtechLtd. of Tulsa, Okla.

As will be recognized by persons of ordinary skill in the art, where thereaction process involves the use of corrosive substances (such as forexample, sulfuric acid or caustic), the tubular reactor and its internalmixing means should be constructed of corrosion resistant materials,including but not limited to stainless steel (e.g., 300 series, 904L,6-moly), tantalum, zirconium, and HASTELLOY® (e.g., B, B-2, B-3, C-22,and C-276).

The reaction medium may be any material suitable for mixing with,containing, and transporting the reactants of the desired chemicalreaction, without being consumed by the reaction, and will depend uponthe nature of the desired chemical reaction and the required reactants.For example, without limitation, a suitable reaction medium may comprisethe same types of compounds as are expected to be produced by thereaction process involving cyanohydrins. In fact, the reaction mediummay be suitably comprised of captured and recycled products of thereaction process. Thus, in the case of a hydrolysis reaction of acetonecyanohydrin and sulfuric acid which is expected to produce SIBAM, HIBAMand MAM, the reaction medium could suitably comprise one or more ofSIBAM, HIBAM and MAM. In some embodiments, the reaction medium mayfurther comprise diluent materials, such as for example, hexane, sulfurdioxide, or straight-chain hydrocarbons.

It is understood that one or more of the reactants (such as, forexample, the acid in a hydrolysis reaction) may be provided indirectlyto the tubular reactor by first adding one or more of the reactants tothe reaction medium prior to providing the reaction medium to thetubular reactor.

The one or more reactants used for the reaction process will depend uponthe desired reaction and reaction products and it is well within theability of persons of ordinary skill to select suitable reactants. Forexample, where it is desired to make SIBAM, HIBAM and MAM for furtherconversion to MAA and esters thereof, suitable reactants may be acetonecyanohydrin and an acid selected from the group consisting of sulfuricacid, oleum and mixtures thereof (as disclosed in US '093 discussedearlier hereinabove). Where acetone cyanohydrin is itself the desiredproduct, the reactants may be acetone and hydrogen cyanide (as describedin Kirk-Othmer, Encyclopedia of Chemical Technology), and a strong base,such as sodium hydroxide, may be present. In this reaction, water mayalso be present as a diluent, and the reaction may be typicallyperformed between 0° C. and 20° C., with elevated temperatures (greaterthan about 20° C.) promoting cyanohydrin decomposition in this reactionsystem. Where it is desired to produce a particular cyanohydrin known asmethyl ethyl ketone cyanohydrin, the reactants may be hydrocyanic acidand methyl ethyl ketone (as disclosed in U.S. Pat. No. 6,743,938), andthe reaction may be performed in the presence of a strong base, such asdiethylamine. Thus, the cyanohydrin may be the reactant or the productin the reaction process and the method of the present invention may beadvantageously applied to any such exothermic reaction process involvingcyanohydrins.

The step of mixing the reaction medium with the one or more reactants toform a bulk reaction mixture having a substantially homogenouscomposition and a substantially homogenous reaction temperature isaccomplished, at least in part, in accordance with the presentinvention, by the use of the tubular reactor having internal mixingmeans described hereinabove.

Another way to rapidly and thoroughly mix the reaction medium and one ormore reactants to form a homogenous bulk reaction mixture, in accordancewith the present invention, would be to provide at least one of thereactants to the tubular reactor at a plurality of points of addition,using a plurality of injector devices, such as without limitation,injector nozzles, that are positioned about the tubular reactorapparatus. The injector devices may be positioned about the tubularreactor circumferentially, longitudinally, or both. Moreover, all of theinjector devices need not be used at any given time, but rather, atleast one, and preferably more than one injector device should be in useto provide at least one of the reactants to the tubular reactor atvarious different points of addition. This arrangement serves todistribute the reactant more evenly into the reaction medium. In aparticular embodiment of the present invention, the injection velocityof the reactant or reactants being provided through the injector devicesmay be the same at each injector device being used. Additionally, theinjection velocity of the reactant(s) may be maintained, for example,without limitation, between 10 ft/sec and 80 ft/sec (3 m/sec and 24m/sec), or between 20 ft/sec and 65 ft/sec (6 m/sec and 20 m/sec), oreven between 28 ft/sec and 42 ft/sec (8.5 m/sec and 13 m/sec), toachieve efficient mixing.

It is also possible, in accordance with the present invention, tomaintain optimal mixing efficiency using the injector devices byoperating fewer injectors at lower overall production rates and,similarly, by operating more of the injector devices at higherproduction rates, rather than using the same number of injector devicesat all times and adjusting the flow rate through each nozzle. The formerprocedure is believed to be better than the latter procedure because thelatter procedure would result in variable injection velocities and,therefore, variable mixing efficiencies, at different locations withinthe reaction zones. For example, operating 10 injector devices atdifferent injection velocities to achieve an overall reactant feed rateof 100 pounds per hour would create variable mixing conditions in thetubular reactor and a non-homogenous bulk reaction mixture. Operating 10injector devices each at 10 pounds per hour would achieve more uniformmixing and a more homogenous bulk reaction mixture. If a decision ismade to decrease the production rate such that only a feed rate of 50pounds per hour of reactant is required, then only 5 of the injectordevices could be operated, each at the same 10 pounds per hour, whilethe other 5 injector devices are disabled or turned off, thusmaintaining uniformity of mixing within the tubular reactor. It isbelieved that further optimization of the foregoing procedures, as wellas the calculations and conversions required to determine the optimalinjector operation procedure, are well within the ability of persons ofordinary skill in the art.

In a particular embodiment of the present invention, which is ahydrolysis reaction of acetone cyanohydrin with sulfuric acid, theaddition rate of a reactant, such as acetone cyanohydrin, is controlledsuch that the temperature at the point of addition is never greater thanthe bulk temperature of the mixed product which leaves the tubularreactor. This serves to minimize, or even eliminate, the hot spots whichmay otherwise develop at the point of addition of the reactants throughthe injector devices.

As with most exothermic reactions, the heat produced by the exothermicreaction process involving cyanohydrins must be removed in order tosustain the reaction process over time in a continuous steady state. Theheat may be removed by cooling the tubular reactor, which will of coursealso cool the reaction zones and the bulk reaction mixture therein,using any conventional cooling means such as for example, any one ormore of the following devices: shell-and-tube heat exchangers, spiralcoolers, plate-and-frame exchangers, jacketed piping sections, andvessels with internal coiling coils or jacketing. It is possible to useturbulators in the tubes of shell-and-tube heat exchangers to improvecooling efficiency and/or resist fouling.

In accordance with the present invention, heat may also be removed fromthe exothermic reaction process by cooling the reaction medium to atemperature between 1° C. and 10° C. less than the bulk temperature ofthe mixed product prior to providing the reaction medium to the tubularreactor. This aspect of the present invention results in the formationof a cooled bulk reaction mixture upon mixing the reactants with thereaction medium in the at least one reaction zone of the tubularreactor, which provides a cooler environment for the cyanohydrin,regardless of whether the cyanohydrin is a reactant that is added, or aproduct that is formed, in the reaction zone.

Additionally, it is advantageous to remove heat from the cyanohydrinswhile they are in the at least one reaction zone with the reactionmedium to minimize their decomposition. In accordance with the method ofthe present invention, this can be accomplished, at least in part, byproviding an excess of reaction medium to the at least one reaction zonein comparison to the amount of reactants provided, whereupon thereaction medium becomes a heat sink and absorbs some of the heat fromthe cyanohydrins. For example, the reaction medium and the one or morereactants may be provided at a ratio of reaction medium:reactants ofbetween 2:1 and 200:1, or between 3:1 and 100:1, or even between 4:1 to40:1. It is noted that higher reaction medium:reactants ratios arebetter because they are believed to provide a larger heat sink capableof absorbing greater quantities of heat.

In another embodiment of the present invention, one or more of thereactants may be cooled prior to being provided to the tubular reactor,for example, using separate heat exchangers (not shown).

Where the exothermic reaction process involving cyanohydrins is ahydrolysis reaction of acetone cyanohydrin and sulfuric acid whichproduces a mixed product comprising SIBAM, HIBAM, and MAM, as previouslydiscussed, for further reaction to produce MAA and esters thereof, themethod may further comprise thermally converting the mixed product fromthe hydrolysis reaction in a cracker reactor to produce a crackerreactor mixture comprising methacrylamide and methacrylic acid. Thecracker reactor mixture may then be reacted in at least one reactor witha material selected from alkanols and water to produce a monomerselected from methacrylic acid and esters thereof. Examples of suitablealkanols include but are not limited to methanol, ethanol, and butanol.

In addition, to the foregoing features, it is possible for persons ofordinary skill in the art to recognize and develop many additions andmodifications to the method of the present invention, all of which areintended to be within the scope of the invention. For example, where theexothermic reaction process is a hydrolysis reaction of acetonecyanohydrin with sulfuric acid, the reaction process may be a two stagesystem, i.e., having two tubular reactors and where the acetonecyanohydrin reactant feed is split between the two reactors, withbetween 50% and 95% of the acetone cyanohydrin reaction being providedto the first reactor, and the remainder to the second reactor.

As might be recognized by persons of ordinary skill, the reactionprocesses involving cyanohydrins may also involve the need to transportand pump process streams which are highly viscous. One or more of thereaction medium and the mixed product may be transported and circulatedthrough and between the process apparatus using high-viscosity servicepumps, such as, but not limited to, Disc pumps (commercially availablefrom Discflo Corporation of Santee, Calif.), positive displacementpumps, or gear pumps. One or more of the reactants, such as the acid ina hydrolysis reaction, may be injected into the reaction medium prior toproviding the reaction medium to the tubular reactor to provide higherlocalized mole ratios and to reduce the viscosity effects.

Conditions in the reaction process, such as where the reaction processis a hydrolysis reaction of acetone cyanohydrin with sulfuric acid, maymake degassing of the mixed product advantageous. In such circumstances,any conventional degassing means is suitable, including but not limitedto, one or more devices selected from the group consisting of:impingement plates, coalescers, baffles, centrifugal separators (such as“Porta-Test Revolution” degassers, from NATCO Group, Inc. of Houston,Tex.), vacuum chambers, distributors, nozzles, throttling valves, flashtanks, settling chambers, ASP-type Degassing Pumps (commerciallyavailable from Yokota Manufacturing Co., Ltd. of Hiroshima, Japan), andthe Kurabo In-line Degassing Device (available from Kurabo IndustriesLtd. of Osaka, Japan).

As would be easily determinable by persons of ordinary skill in the art,it may also be advantageous to add one or more polymerization inhibitorsto the reaction process, such as, for example, to one or more of thereactants prior to providing them to the tubular reactor. Suitablepolymerization inhibitors will depend, at least in part, upon the typesof reactants and products involved in the reaction process. For example,where the exothermic reaction process is a hydrolysis reaction ofacetone cyanohydrin with sulfuric acid, a suitable inhibitor wouldinclude, but not be limited to, phenothiazine.

Furthermore, where the exothermic reaction process is a hydrolysisreaction of acetone cyanohydrin with sulfuric acid, the molar ratio ofacid:acetone cyanohydrin present in the bulk reaction mixture is in therange of from 1.3:1 to 1.9:1

These and other similar modifications will readily suggest themselves tothose skilled in the art, and are intended to be encompassed within thespirit of the present invention disclosed herein and the scope of theappended claims.

EXAMPLES

The following Examples provide comparative yields for twocommercial-scale hydrolysis reaction processes operating at identicalconditions. The results of these Examples demonstrate the yieldadvantage afforded by the method of the present invention over the priorart CSTR-based reaction processes involving cyanohydrins, particularlywhen applied to a hydrolysis reaction of acetone cyanohydrin withsulfuric acid. The compositions of the acetone cyanohydrin reactant andsulfuric acid reactant were the same for both Example 1 and Example 2.

Example 1 Comparative—Prior Art Process

A first hydrolysis process (“Prior Art”) of the type disclosed inKirk-Othmer and US '093 is illustrated by FIG. 2, and comprised two CSTRreactors in series. This system was operated at an H2SO4:ACH molar ratioof 1.48, and at a 2.3:1 ACH addition split, wherein 70% by weight of thetotal ACH feed was added to the first reaction stage, and 30% by weightof the total ACH feed was added to the second reaction stage. Sulfuricacid at a concentration of 99.5% and ACH at a concentration of 98.5%were utilized as reactants in this system.

Specifically, the 1^(st) reaction stage of the hydrolysis systememployed in this example comprised a 1^(st) stage CSTR 230, acentrifugal pump 210, a heat exchanger 220, and associated 1^(st) stagecirculation piping (203,204,205). CSTR 230 comprised a 5000 gal (19cubic meters) vessel and a dual-impeller, pitched-blade agitator forhigh-efficiency mixing of the reactor contents. Sub-surface ACH additionto the 1^(st) stage CSTR 230 was provided via 201 using a firstdip-pipe. Similarly, Sub-surface Sulfuric Acid addition to the 1^(st)stage CSTR 230 was provided via 202 using a second dip-pipe. Thesedip-pipes served to direct the flow of reactants into the turbulent zonenear the tip of the agitator blades in order to maximize efficiency ofthe mixing. PTZ inhibitor in acetone solution (not shown) was also addedinto CSTR 230 to retard polymer formation. The temperature of the bulkliquid in the bottom of CSTR 230 could be monitored using thermocoupleT230.

Stream 203 provides hydrolysis mix to Pump 210, which then circulatedhydrolysis mix through the 1^(st) stage circulation piping at acontinuous rate of about 2.8 million lbs/hr (i.e., 4000 gpm, 15,140liters/min). Stream 204 conveyed the hydrolysis mix from the dischargeof pump 210 to heat exchanger 220, where it was cooled. Heat exchanger220 was a shell-and-tube type exchanger, with the process flow(hydrolysis mix) passing through the shell side and a nominal 60° C.tempered water flow passing through the tube side. Cooled hydrolysis mixexited the heat exchanger via stream 205 and was returned to CSTR 230.Gases removed from the hydrolysis mix were vented to a process flareheader (not shown) for disposal. Degassed hydrolysis mix overflowed fromthe side of CSTR 230 and was conveyed forward to the 2^(nd) reactionstage via stream 209.

The 2^(nd) reaction stage of the hydrolysis system employed in thisexample comprised a 2^(nd) stage CSTR 260, a centrifugal pump 240, aheat exchanger 250, and associated 2 stage circulation piping(213,214,215). CSTR 260 comprised a 5000 gal (19 cubic meters) vesseland a dual-impeller, pitched-blade agitator for high-efficiency mixingof the reactor contents. Sub-surface ACH addition to the 2^(nd) stageCSTR 230 was provided via 211 using a first dip-pipe. OptionalSub-surface Sulfuric Acid (212) addition to the 2^(nd) stage CSTR 230was not used in this example. As with the 1^(st) stage CSTR dip-pipes,these 2^(nd) stage dip-pipes served to direct the flow of reactants intothe turbulent zone near the tip of the agitator blades in order tomaximize efficiency of the mixing. The temperature of the bulk liquid inthe bottom of CSTR 260 could be monitored using thermocouple T260.

Stream 213 provided hydrolysis mix to Pump 240, which then circulatedhydrolysis mix through the 2^(nd) stage circulation piping at acontinuous rate of about 4.2 million lbs/hr (i.e., 6000 gpm, 22,700liters/min). Stream 214 conveyed the hydrolysis mix from the dischargeof pump 240 to heat exchanger 250, where it was cooled. Heat exchanger250 was a shell-and-tube type exchanger, with the process flow(hydrolysis mix) passing through the shell side and a nominal 65° C.tempered water flow passing through the tube side. Cooled hydrolysis mixexited the heat exchanger via stream 215 and was returned to CSTR 260.Gases removed from the hydrolysis mix were vented to a process flareheader (not shown) for disposal. Degassed hydrolysis mix overflowed fromthe side of CSTR 260 and was conveyed forward to the cracker reactor(100) via Stream 219.

In this example, the bulk temperature of the reaction mixture exitingthe 1^(st) reaction stage CSTR (230), as measured by thermocouple T230,was held constant at 85° C.; the bulk temperature of the reactionmixture exiting the 2^(nd) reaction stage CSTR (260), as measured bythermocouple T260, was held constant at 101° C.

Under steady state conditions, samples of the final hydrolysis mix werecollected from stream 219 using well-insulated sample containers(Thermos™ brand vacuum bottles).

An aliquot (˜10 g) of the representative Hydrolysis mix was removed andplaced in a tared jar containing a stir bar and its weight was recorded.Methanesulfonic acid (99.5% purity, ˜3 g, from Aldrich Chemical Company)was added as an internal standard via a syringe and the weights were allrecorded. The mixture was stirred in a constant temperature water bathat 60° C. for 40 min. An aliquot (˜0.2 g) of the resulting mixture wasremoved and placed in an NMR tube and diluted with deuteratednitromethane (CD₃NO₂, from Aldrich Chemical Company). The clear andhomogeneous mixture was analyzed by NMR on a Varian Inova 500Instrument.

The total molar yield of SIBAM, HIBAM and MAM produced by the foregoingprocess is reported in Table 1.

Example 2

An improved hydrolysis system (“Inventive”), in accordance with themethod of the present invention, is illustrated in FIG. 1 and comprisedtwo continuous flow reaction stages. This system was operated under thesame conditions used for the CSTR-based hydrolysis system of thepreceding Example 1.

Specifically, this improved hydrolysis system was operated at anH2SO4:ACH molar ratio of 1.48, and at a 2.3:1 ACH addition split,wherein 70% by weight of the total ACH feed was added to the firstreaction stage and 30% by weight of the total ACH feed was added to thesecond reaction stage. As in the previous example, Sulfuric acid at aconcentration of 99.5% and ACH at a concentration of 98.5% were utilizedas reactants.

The 1^(st) reaction stage of the hydrolysis system employed in thisexample comprised an ACH mixing apparatus 10, a degassing apparatus 20,a centrifugal pump 30, a heat exchanger 40, and associated 1^(st) stagecirculation piping (3,4,5,7,8). Sulfuric Acid (6) was added into thehydrolysis mix in stream 5 through a mixing tee. Stream 5 providedhydrolysis mix to Pump 30, which then circulated hydrolysis mix throughthe 1^(st) stage circulation piping at a continuous rate of about 2.5million lbs/hr (i.e., 3500 gpm, 13,250 liters/min). Stream 7 conveyedthe hydrolysis mix from the discharge of pump 30 to heat exchanger 40,where it was cooled. Heat exchanger 40 was a shell-and-tube typeexchanger, with the process flow (hydrolysis mix) passing through theshell side and a nominal 60° C. tempered water flow passing through thetube side. Cooled hydrolysis mix exited the heat exchanger via stream 8.The temperature of the cooled hydrolysis mix could be monitored usingthermocouple T8. The hydrolysis mix then entered the ACH mixingapparatus 10, wherein ACH was added into the hydrolysis mix stream. TheACH mixing apparatus 10 comprised a single static mixing unit consistingof four Koch SMXL mixing elements (available from Koch-Glitsch, Inc. ofWichita, Kans.) installed in series within a 12″ diameter pipingsection. The static mixing unit was approximately 190 inches in length.The ACH mixing apparatus 10 further comprised two sets of ACH injectors:a first set of four injectors 11 located at a distance of about 30″ fromthe inlet end of the mixing apparatus and a second set of four injectors12 located at a distance of about 45″ from the inlet end of the mixingelement. Each of the four injectors in a set were evenly-spaced alongthe circumference of the pipe section—e.g., one injector each positionedat 0°, 90°, 180°, and 270° relative to the pipe section centerline. Eachinjector comprised a 0.290″ internal diameter orifice, flush-mounted tothe piping section wall, through which liquid ACH flowed at a velocityof about 36 feet per second (11 meters per second) into the staticmixing unit. At this velocity, a jet of ACH was produced havingsufficient kinetic energy to traverse from the pipe section wall towardthe centerline of the static mixing unit, thereby ensuring rapid andefficient mixing. For the operating rate of this specific example, sixof the eight injectors were utilized: all four of the first set ofinjectors and two of the second set of injectors. Of the injectors inoperation, all were operated at the same ACH flow rate. As a result ofthe exothermic ACH hydrolysis reaction, the hydrolysis mix warmed withinthe ACH mixing apparatus. The warm hydrolysis mix exited the ACH mixingapparatus via stream 3 and entered the degassing apparatus 20. PTZinhibitor in acetone solution (9) was added into the hydrolysis mixstream 3 to retard polymer formation.

Degassing apparatus 20 comprised an unagitated 5,600 gallon (21 cubicmeters) degassing vessel in which was installed a “Porta-TestRevolution” model centrifugal gas/liquid separator (designed andmanufactured by NATCO Group, Inc. of Houston, Tex.). Gases removed fromthe hydrolysis mix were vented to a process flare header (not shown) fordisposal; the degassed hydrolysis mix collected as a bulk liquid in thebottom of the degassing vessel. The temperature of the bulk liquid inthe bottom of the degassing vessel could be monitored using thermocoupleT20. Degassed hydrolysis mix was withdrawn from the bottom of thedegassing vessel and was divided into two streams: stream 49 conveyed afirst portion of the hydrolysis mix forward to the 2^(nd) reactionstage, while stream 5 returned a second portion of the hydrolysis mix tocentrifugal pump 30 to maintain the 1^(st) stage circulation.

The 2^(nd) reaction stage of the inventive hydrolysis system employed inthis example comprised an ACH mixing apparatus 50, a degassing apparatus60, a centrifugal pump 70, a heat exchanger 80, and associated 2^(nd)stage circulation piping (13,14,15,17,18). Hydrolysis mix from stream 49entered the 2^(nd) stage and was combined with the hydrolysis mix instream 15. In this specific example, optional sulfuric acid (16) was notadded. Stream 15 provided hydrolysis mix to Pump 70, which thencirculated hydrolysis mix through the 2^(nd) stage circulation piping ata continuous rate of about 2.2 million lbs/hr (i.e., 3000 gpm, 11,360liters/min). Stream 17 conveyed the hydrolysis mix from the discharge ofpump 70 to heat exchanger 80, where it was cooled. Heat exchanger 80 wasa shell-and-tube type exchanger, with the process flow (hydrolysis mix)passing through the tube side and a nominal 70° C. tempered water flowpassing through the shell side. Cooled hydrolysis mix exited the heatexchanger via stream 18. The temperature of the cooled hydrolysis mixcould be monitored using thermocouple T18. The hydrolysis mix thenentered the ACH mixing apparatus 50, wherein ACH was added into thehydrolysis mix stream. The ACH mixing apparatus 50 comprised a singlestatic mixing unit consisting of four Koch SMXL mixing elementsinstalled in series within a 12″ diameter piping section. The staticmixing unit was approximately 210 inches in length. The ACH mixingapparatus 50 further comprised two sets of ACH injectors: a first set offour injectors 11 located at a distance of about 30″ from the inlet endof the mixing apparatus and a second set of four injectors 12 located ata distance of about 45″ from the inlet end of the mixing element. Eachof the four injectors in a set were evenly-spaced along thecircumference of the pipe section—e.g., one injector each positioned at0°, 90°, 180°, and 270° relative to the pipe section centerline. Eachinjector comprised a 0.175″ internal diameter orifice, flush-mounted tothe piping section wall, through which liquid ACH flowed at a velocityof about 62 feet per second (19 meters per second) into the staticmixing unit. At this velocity, a jet of ACH was produced havingsufficient kinetic energy to traverse from the pipe section wall towardthe centerline of the static mixing unit, thereby ensuring rapid andefficient mixing. For the operating rate of this specific example, onlythe first set of four injectors were utilized; of the injectors inoperation, all were operated at the same ACH flow rate. As a result ofthe exothermic ACH hydrolysis reaction, the hydrolysis mix warmed withinthe ACH mixing apparatus. The warm hydrolysis mix exited the ACH mixingapparatus via stream 13 and entered the degassing apparatus 60. In thisspecific example, optional PTZ inhibitor in acetone solution (19) wasnot added.

Degassing apparatus 60 comprised an unagitated 10,900 gallon (41 cubicmeters) degassing vessel in which was installed a “Porta-TestRevolution” model centrifugal gas/liquid separator (designed andmanufactured by NATCO Group, Inc. of Houston, Tex.). Gases removed fromthe hydrolysis mix were vented to a process flare header (not shown) fordisposal; the degassed hydrolysis mix collected as a bulk liquid in thebottom of the degassing vessel. The temperature of the bulk liquid inthe bottom of the degassing vessel could be monitored using thermocoupleT60. Degassed hydrolysis mix was withdrawn from the bottom of thedegassing vessel (14) and was divided into two streams: stream 99conveyed a first portion of the hydrolysis mix forward to the crackerreactor (100), while stream 15 returned a second portion of thehydrolysis mix to centrifugal pump 70 to maintain the 2^(nd) stagecirculation.

In this example, the bulk temperature of the reaction mixture exitingthe 1^(st) stage degassing apparatus (20), as measured by thermocoupleT20, was held constant at 85° C.; the bulk temperature of the reactionmixture exiting the 2^(nd) stage degassing apparatus (60), as measuredby thermocouple T60, was held constant at 101° C.

Under steady state conditions, samples of the final hydrolysis mix werecollected from stream 99 using well-insulated sample containers(Thermos™ brand vacuum bottles).

As in the previous example, the hydrolysis mix sample was acidified,diluted, and analyzed by NMR. The total molar yield of SIBAM, HIBAM andMAM produced by the foregoing inventive method is reported in Table 1.

TABLE 1 Stream Temperature Hydrolysis at ACH Feed point Residence ACHMolar System 1^(st) stage 2^(nd) stage Time Yield (%) Example 1 85° C.101° C.  40 minutes 95.23 ± 0.60 (Prior Art CSTR) (T230) (T260) (FIG. 2)Example 2 79° C. 100° C. 110 minutes 96.01 ± 0.22 (Inventive Method)(T8)  (T18)  (FIG. 1)This comparative example illustrates that the inventive continuous flowreaction system provides a higher ACH yield than the prior-artCSTR-based system when used to perform ACH Hydrolysis reactions.

1. A method for minimizing decomposition of cyanohydrins in anexothermic reaction process which produces cyanohydrins and a quantityof heat, said cyanohydrins being selected from the group consisting ofacetone cyanohydrin and methyl ethyl ketone cyanohydrin, said methodcomprising the steps of: (a) providing a reaction medium to a tubularreactor containing at least one reaction zone therein and havinginternal mixing means positioned in said at least one reaction zone; (b)providing one or more reactants to said tubular reactor; (c) mixing saidreaction medium with said one or more reactants in said at least onereaction zone, thereby forming a bulk reaction mixture having asubstantially homogenous composition and a substantially homogenousreaction temperature; (d) removing a quantity of heat from theexothermic reaction process, said quantity of heat being equivalent tosaid quantity of heat produced by the exothermic reaction process; and(e) reacting said one or more reactants in said at least one reactionzone to produce a mixed product having a bulk temperature.
 2. The methodof claim 1, wherein the step of removing a quantity of heat is performedby cooling said reaction medium to a temperature between 1° C. and 10°C. less than said bulk temperature prior to providing said reactionmedium to said tubular reactor.
 3. The method of claim 1, wherein saidinternal mixing means is at least one device selected from the groupconsisting of: static mixers, orifice plates, venturis, jet mixers,eductors, perforated plates, spargers, agitators, rotary mixers,high-velocity circulation loops, and spray nozzles.
 4. The method ofclaim 1, wherein said tubular reactor comprises at least two tubularreactors.
 5. The method of claim 3, wherein the static mixer comprisesone or more mixing element selected from the group consisting of:blades, pins, baffles, tabular inserts, and other shear-inducingdevices.
 6. The method of claim 1, wherein the cyanohydrins producedcomprise acetone cyanohydrin, and wherein said one or more reactantscomprise a first reactant comprising acetone and a second reactantcomprising hydrogen cyanide.
 7. The method of claim 1, wherein thecyanohydrins produced comprise methyl ethyl keton cyanohydrin, andwherein said one or more reactants comprises a first reactant comprisingmethyl ethyl ketone and a second reactant comprising hydrogen cyanide.8. The method of claim 1, wherein a strong base is present.
 9. Themethod of claim 8, wherein said strong base is selected from the groupconsisting of sodium hydroxide and diethylamine.
 10. The method of claim1, wherein said exothermic reaction is performed between 0° C. and 20°C.
 11. The method of claim 1, wherein said step of removing a quantityof heat from the exothermic reaction process is accomplished using oneor more devices selected from the group consisting of: a shell-and-tubeheat exchanger, a spiral cooler, a plate-and-frame heat exchanger, ajacketed piping section, a vessel with internal cooling coils and avessel with external jacketing.
 12. The method of claim 11, wherein ashell-and-tube heat exchanger includes the tubular reactor and thedevice for removing a quantity of heat.